The present invention relates generally to wind deflector apparel. More particularly, it concerns a device for smoothly redirecting wind away from the ear for the purpose of decreasing any personally heard wind noise generated by air flow past the ear and head, while at the same time permitting ambient sound to pass through unattenuated.
There are two main sources of perceived wind noise. In a head wind the first source is due to the shape of the head causing turbulence just behind the cheek bone, and is mainly responsible for the very low frequency noise. The second source appears to be due to stream flow by the concha which is the shallow cavity inside the ear just adjacent to the sensitive ear canal, and is apparently responsible for the higher frequency noise.
At low wind speeds, the combined noise spectrum creates a personal rumbling in the ear canal which gets louder and also higher in frequency as the wind speed increases. Unweighted measurements have been made of the noise created in the concha by the use of a microphone probe apparatus. See, U. R. Kristiansen, O.K..phi.. Pettersen 1978 Journal of Sound and Vibration, "Experiments On The Noise Heard By Human Beings When Exposed To Atmospheric Winds", 58(2)285-291. For an average person facing a 21 mile per hour (mph) wind the noise spectrum was found to extend below 25 cycles per second (Hz) to about 150 Hz at an intensity of 92 decibels (db) above quiet hearing threshold. The noise spectrum then tapers off in intensity to 60 db at 2400 Hz. Articulation tests have shown that the band of speech frequencies most important for intelligibility is that extending from about 500 to 2500 Hz. The signal to noise ratio of speech to wind induced ear canal noise can significantly deteriorate for winds above 20 mph. This comes as no surprise to hard of hearing sufferers who have lost their high frequency sensitivity and must completely rely on the lower part of the hearing spectrum. Even bike riders, sailors, skiers, etc. with good hearing may have considerable difficulty hearing ambient sounds such as traffic, conversation between companions, safety warnings and certain sounds of nature. High relative wind speeds are not uncommon, e.g., by bicycling 15 mph into a 15 mph atmospheric wind the relative headwind is 30 mph. Then too, for those who simply stand still on a windy day, such as pedestrians, construction workers and field workers, the same noise can be heard with additional low frequency pulses.
There is the additional problem of fatigue. The apparent intensity of the wind seems to be greater when it can also be heard. Constant and especially gusty wind noise over a long period of time can create considerable fatigue, which if not corrected can reduce the enjoyment of an activity and can even turn to irritation. Worse, fatigue can also be a contributing factor in creating misjudgments and accidents. Some children are quite susceptible to wind induced noise in the ear.
For the most part, this is a problem people have learned to live with. Mechanical devices such as ear plugs and ear muffs are designed to protect the ear against very loud machinery noises. By their very nature they are not completely sound permeable but contain a considerable amount of sound resistant material.
Heavy duty earmuffs, that are primarily designed to warm the ears, generally handle wind noise abatement as a secondary feature. For instance, Geiser, U.S. Pat. No. 4,582,374, provides for open ventilator holes drilled or cast through an otherwise solid, heat insulated protecting case. The uncovered holes are exposed to the windstream alongside the head (such as during skiing); and because they are open and uncovered to the outside, each hole becomes a wind noise generator. Such heavy duty earmuffs are uncomfortable to wear in the summer.
Simpler, more traditional ear cover paraphernalia include wool caps, flat earmuffs, and headbands which pass over and press on the ear flange. By necessity, they must be somewhat snug in order to keep out the wind. The popularity of these apparel notwithstanding, many people do not like their ears pressed against their heads and prefer to go without protection.
From an aeroacoustical standpoint, depending on the surface material used, headbands and caps are fairly efficient in eliminating mid and high frequency wind noise (the blowing sound "WH") because they divert the airflow past the external ear where that specific noise is generated. But the elimination of the low frequency rumble is elusive. Heavier materials are currently being used in some common earmuffs to address this problem but the ambient high frequency sound transmission to the ear is compromised. Ironically, it is the high frequencies that allow the external ear to sense fore and aft direction of the sound source accurately, an important safety feature on the work site.
Attempts at low frequency wind noise abatement are not new. In 1954, Hayes and Cudworth* published experimental data concerning a crude windscreen design which was tested at the Acoustics Laboratory, Massachusetts Institute of Technology, under contract with the Air Force. (J. R. M. Hayes and A. L. Cudworth (1954), letters to the editor "Windscreen for the Ear" J. Acoust. Soc. Am. 26, 254-5.) The windscreen was made up of two cylindrical cups, each 23/4" diameter by 31/2" long (20 cubic inches each). The surface, made of woven nylon cloth with negligible ambient sound attenuation, was stretched over a 1/4" mesh screen matrix. Standard earphone cushions and an earphone headband provided sealed contact with the head.
Partial results of the test show that at a wind speed of 20 mph, the windscreen attenuated the wind noise of the unprotected ear canal by an average of 21 decibels (dB) at 200 cycles per second (Hz), and 13 dB at around 500 Hz. This is a significant drop in noise level, especially at the lower frequency. However, people will likely not wear such unwieldy cylinders over their ears when they can use the less effective but much simpler headband.